The present invention relates generally to antenna systems, and more particularly. to a communication satellite antenna system having an improved dual function subreflector.
Conventional dual reflector antenna systems, and in particular those that are used in satellite-based communication antenna systems, operate with optimum performance for beams that cover a desired coverage areas as viewed from one specific orbital position. Operation of the satellite in more than one orbital position has resulted in performance reduction due to the fact that the antenna system is a compromised between orbital positions.
It is an objective of the present invention to overcome this limitation of such conventional dual reflector antenna systems. It is also an objective of the present invention to provide for a communication satellite antenna system having an improved dual function subreflector.
The present invention provides for an improved satellite-based antenna system that employs an improved dual function subreflector. The present invention provides optimum performance from a dual reflector antenna when operating in two or more different satellite positions, with no compromise to the performance for either mode of operation.
An exemplary antenna system comprises a flat plate dual function subreflector and a subreflector positioning mechanism that selectively positions the subreflector at predetermined positions corresponding to two or more operational positions of the satellite. A plurality of feed arrays couple energy to and from the subreflector, and a main reflector generates beams for desired coverage areas.
In a dual reflector antenna system, the selected orientation of the flat plate subreflector maps the equivalent focal point of the main reflector to a position within a selected feed array. The size and position of each feed radiator in a selected feed array is optimized to form one or more beams generated from the antenna system for coverage areas as viewed from the selected orbital position of the satellite.
When using the present antenna system, the same coverage area may be provided from different orbital positions of the satellite. In addition, two or more totally different and independent coverage areas may be provided from the satellite that parks on the same or different orbital locations.
The antenna system thus comprises a flat plate subreflector that is oriented to xe2x80x9csteerxe2x80x9d the focal point of a main reflector so that different feed arrays can b used to provide a set of beams for operation from the satellite in different orbital positions. The performance of the antenna system for each orbital position is individually optimized. independent of the other feed array(s).
An advantage of using this configuration for a communication antenna is that the optimum performance for each satellite orbital position of operation results in the highest antenna gain achievable and results in the highest Effective (Equivalent) Isotropic Radiated Power (EIRP) and gain-to-system noise temperature (G/T) for the communication system. The sidelobe structure of each beam is also optimum and results in reduced interference.